In a new study, researchers for the first time establishes a link between infection with the bovine leukemia virus and human breast cancer. The research was published in the journal PLOS ONE.
In the study, researchers analyzed breast tissue from 239 women, comparing samples from women who had breast cancer with women who had no history of the disease for the presence of bovine leukemia virus (BLV). They found that 59 percent of breast cancer samples had evidence of exposure to BLV, as determined by the presence of viral DNA. By contrast, 29 percent of the tissue samples from women who never had breast cancer showed exposure to BLV.
Bovine leukemia virus infects dairy and beef cattle's blood cells and mammary tissue. The retrovirus is easily transmitted among cattle primarily through infected blood and milk, but it only causes disease in fewer than 5 percent of infected animals.
A 2007 U.S. Department of Agriculture survey of bulk milk tanks found that 100 percent of dairy operations with large herds of 500 or more cows tested positive for BLV antibodies. This may not be surprising since milk from one infected cow is mixed in with others. Even dairy operations with small herds of fewer than 100 cows tested positive for BLV 83 percent of the time.
What had been unclear until recently is whether the virus could be found in humans, something that was confirmed in a study last year in Emerging Infectious Diseases. That paper overturned a long-held belief that the virus could not be transmitted to humans.
The new paper takes the earlier findings a step further by showing a higher likelihood of the presence of BLV in breast cancer tissue. When the data was analyzed statistically, the odds of having breast cancer if BLV were present was 3.1 times greater than if BLV was absent.
The researchers emphasized that this study does not identify how the virus infected the breast tissue samples in their study. The virus could have come through the consumption of unpasteurized milk or undercooked meat, or it could have been transmitted by other humans.
Based on material originally posted by University of California - Berkeley.